Any tips for start contacting with celebrities?

[♥Arianator4Life♥]

So I know that the chance of doing this and getting noticed are very low, but I just want to give it a shot. I've never done this in my life, too. What I want to do is getting noticed by celebrities in twitter, Facebook, YouTube or other stuff, but I'm super nervous and don't know how to start contacting. First celebrity crush I ever had was Ariana Grande, she is my only favorite celebrity and I love her a lot, but the thing is, if celebrities have no idea who you are or existence, how do you get that going? I don't want to feel embarrassed about myself .-. btw I'm 17 years old.

I also don't want any troll( ex. your just wasting time, no way that will ever happen, etc...). Any tips would be very pleased ;D